Abstract
BackgroundBacterial genomes harbour a large number of tandem repeats, yet the possible phenotypic effects of those found within the coding region of genes are only beginning to be examined. Evidence exists from other organisms that these repeats can be involved in the evolution of new genes, gene regulation, adaptation, resistance to environmental stresses, and avoidance of the immune system.ResultsIn this study, we have investigated the presence and variability in copy number of intragenic tandemly repeated sequences in the genome of Legionella pneumophila, the etiological agent of a severe pneumonia known as Legionnaires' disease. Within the genome of the Philadelphia strain, we have identified 26 intragenic tandem repeat sequences using conservative selection criteria. Of these, seven were "polymorphic" in terms of repeat copy number between a large number of L. pneumophila serogroup 1 strains. These strains were collected from a wide variety of environments and patients in several geographical regions. Within this panel of strains, all but one of these seven genes exhibited statistically different patterns in repeat copy number between samples from different origins (environmental, clinical, and hot springs).ConclusionThese results support the hypothesis that intragenic tandem repeats could play a role in virulence and adaptation to different environments. While tandem repeats are an increasingly popular focus of molecular typing studies in prokaryotes, including in L. pneumophila, this study is the first examining the difference in tandem repeat distribution as a function of clinical or environmental origin.
Highlights
Bacterial genomes harbour a large number of tandem repeats, yet the possible phenotypic effects of those found within the coding region of genes are only beginning to be examined
While these Gram-negative bacteria can multiply free-living in culture, it is widely accepted that intracellular replication in amoebic hosts such as Acanthamoeba, Naegleria, or Hartmanella is essential for the propagation and dissemination of L. pneumophila [15]
Evidence exists from other organisms that variable number tandem repeats are involved in the evolution of new genes, gene regulation, adaptation, resistance to environmental stresses, and avoidance of the immune system
Summary
Bacterial genomes harbour a large number of tandem repeats, yet the possible phenotypic effects of those found within the coding region of genes are only beginning to be examined. We have investigated the presence and distribution of tandemly repeated sequences in the genome of the opportunistic pathogen, Legionella pneumophila, the etiological agent of Legionnaires' disease This microorganism flourishes naturally in fresh water environments, but is frequently found in artificial water systems, which are considered the main source of Legionella infections in humans [14]. The L. pneumophila species comprises over 15 serogroups, of which serogroup 1 is responsible for the majority of human infections While these Gram-negative bacteria can multiply free-living in culture, it is widely accepted that intracellular replication in amoebic hosts such as Acanthamoeba, Naegleria, or Hartmanella is essential for the propagation and dissemination of L. pneumophila [15]. L. pneumophila infections end in an acute and severe, often fatal, pneumonia, if not quickly and correctly diagnosed
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